1. Field of the Invention
This invention relates to a device for connecting a tractor to a semitrailer, this device using, in a known manner, a fifth wheel fixed to the tractor, on which the front part of the semitrailer rests.
2. Description of the Prior Art
It is known that the suspension of a tractor and semitrailer combination must take into account contradictory conditions: to provide satisfactory holding of the road regardless of the load of the rig and, in addition, provide suspension for the tractor traveling by itself as well as for the fully loaded rig which calls for a sufficiently stiff suspension.
Moreover, tractors with semitrailers are subjected, during traveling, to a movement called "curling". This movement corresponds to a gallop of the rig and proves detrimental to the comfort of the cab with regard to vibrations.
Detailed studies have shown that the semitrailer, by its characteristics of weights, inertias and suspension stiffnesses, is the cause of this curling movement.
Insulating the body of the semitrailer from the tractor frame by a suspension stage has not made it possible to overcome this problem. To suspend the semitrailer in this way amounts to a decoupling of the vibratory movements of the tractor and those of the semitrailer. This is equivalent, for the vehicle, to rolling empty and therefore results in a very disagreeable dynamic behavior.